private void bntBatDau_Click(object sender, EventArgs e)
        {
            switch (listBox1.SelectedIndex)
            {
                case 0:
                    Phan5.CacSoDen100000 fr0 = new Phan5.CacSoDen100000();
                    fr0.ShowDialog(this);
                    break;
                case 1:
                    Phan5.CacSoDen100ktt fr1 = new Phan5.CacSoDen100ktt();
                    fr1.ShowDialog(this);
                    break;
                case 2:
                    Phan5.BonPhepTinh100000 fr2 = new Phan5.BonPhepTinh100000();
                    fr2.ShowDialog(this);
                    break;
                case 3:
                    Phan5.BonPhepTinhtt fr3 = new Phan5.BonPhepTinhtt();
                    fr3.ShowDialog(this);
                    break;
                case 4:
                    Phan5.HinhHoc.CacDaiLuong fr4 = new Phan5.HinhHoc.CacDaiLuong();
                    fr4.ShowDialog(this);
                    break;
                case 5:
                    Phan5.HinhHoc.OnTapHinhHoc fr5 = new Phan5.HinhHoc.OnTapHinhHoc();
                    fr5.ShowDialog(this);
                    break;
                case 6:
                    Phan5.HinhHoc.OnTapHinhHoctt fr6 = new Phan5.HinhHoc.OnTapHinhHoctt();
                    fr6.ShowDialog(this);
                    break;
                case 7:
                    Phan5.HinhHoc.OnTapVeGiaToan fr7 = new Phan5.HinhHoc.OnTapVeGiaToan();
                    fr7.ShowDialog(this);
                    break;
                case 8:
                    Phan5.LTChung fr9 = new Phan5.LTChung();
                    fr9.ShowDialog(this);
                    break;
                case 10:
                    Phan5.LTChungtt fr10 = new Phan5.LTChungtt();
                    fr10.ShowDialog(this);
                    break;

            }
        }
 private void button1_Click(object sender, EventArgs e)
 {
     Phan5.BonPhepTinhtt fr = new Phan5.BonPhepTinhtt();
     fr.Show();
 }